can vs could: more than past and present forms

Both can and could might sometimes get you confused, but here is the way to deal with them:

can and could are called modal verbs. Modal verbs are used to talk about ability; to show belief in possibility, certainty and probability; to make offer and request; and to ask permission. Other modal verbs are may, might, shall, should, will, would, must.

Modal verbs do not usually stand alone, and if they do, the main verbs are inferred.

Examples:

Q: Can you sing the national anthem offhand?
A: I can (sing the national anthem offhand).

Present and past tense forms

can is the present form while could is the past form.

Examples:

I can tell him if you want me to.

He said he could have done the job if permitted.

can and could generally show ability and possibility, while their negative forms (cannot/can’t; could not/couldn’t) show inability and impossibility.

possibility:

Examples:

It can be very hot in dry season.

It could be very hot in dry season.

If the missing national budget is not found, we could get angry.

We could have joined KOWA party if we were invited.

impossibility:

Examples:

We can’t cope with dollar appreciation against naira anymore.

We couldn’t help him at that time of the year.

ability:

Examples:

I can speak Arabic fluently.

She could eat Sharwama three times daily before she met him.

inability:

Examples:

I can’t tell you.

Oghenekaro couldn’t contest for the election.

Other roles

These verbs are also used to ask for permission or make request and offer.

Examples:

Can I ask a question, please?

Could I ask a question, please?

I can do that for you if you don’t mind.

I could do that for you if you don’t mind.

The above examples are acceptable. However, could is formal and more polite than can.

In summary, can and could are used for present and past situations respectively; could could also be used to talk about a future possibility or make polite request in the present.